The present invention relates generally to a device for determining the clotting time of whole blood and in particular to such a device which incorporates all the elements necessary to determine the clotting time into a compact hand held unit so as to permit the determination to be made at the patient's bedside.
The time it takes for whole blood to clot is an important factor in the conduct of various medical treatments or in the diagnosis of certain diseases. For example, knowledge of the clotting time of whole blood is essential for any patient undergoing heparin therapy which involves the administration of heparin to reduce the ability of the blood to clot. Such cases, for example, include patients undergoing treatment for thromboembolic disease or for those undergoing dialysis which involves the circulation of blood outside the body through a dialysis machine. The clotting time factor is also used in the diagnosis of certain diseases, such a hemophilia, Christmas disease and VonWillebrand's disease.
A general discussion of the technique for determining the clotting time of whole blood and its use in medical treatment and diagnosis is described generally in the American Journal of Clinical Pathology, volume 66, pages 899-940, 1976 and the Journal of the American Medical Association of May 2, 1966, volume 196 at pages 150-154. Briefly, the test involves the drawing of a small quantity (2 milliliters) of venous blood into a warmed tube containing diatomaceous earth. The tube is gently agitated to permit mixing and thereafter gently agitated at periodic intervals until the first definite clot is formed. The time interval between the appearance of blood in the tube and the first unmistakable clot is the activated coagulation time or the ACT. Throughout the entire procedure, the tube and its contents should be maintained at 37.degree. C.
Heretofore, the equipment used to perform the test consisted of a water bath or preheated block, a timer calibrated in one second intervals and a thermometer. All this equipment made the test awkward if not difficult to perform at the patient's bedside. In addition, the need for periodically withdrawing the tube from the bath or heat block to inspect for clots detracted from the maintenance of the desired temperature of the samples throughout the test procedure. Also, just when the first definitive clot begins to form is a subjective determination which could be facilitated by continuous observation of the sample. However, equipment heretofore used did not make such continuous observation possible in that if either a heating block or water bath is used, the sample must be removed to inspect for clots and then returned in order to maintain the sample at temperature.
The present invention, in contrast to prior apparatus used, provides a portable unit to perform the test wherein the unit is capable of performing the heating and timing function of the test while allowing continuous observation of the sample. All these functions are incorporated into a hand held unit which permits the test to be conveniently conducted at the patient's bedside and which permits the sample to be agitated as required by the test.